The RTX-12A and RTX12OEM are half-duplex 1200 baud radio modems designed especially for telemetry and remote data transfer applications. While the standard RTX modem is Bell 202 compatible, an optional CCITT v.23 model is available by special order. The RTX modems provide an inexpensive solution to interfacing computers and microcontrollers to radio links. The modem utilizes FSK audio tones to provide reliable communications over narrow bandwidth channels.

The modem is easily interfaced to radios designed for either telemetry or voice communication. It is suitable for hand-held, mobile or base radios. The data interface is designed to be compatible with both standard RS-232 levels and CMOS logic levels. The total power consumption is less than 25 milliwatts, making it ideal for battery powered applications. When operated from a standard RS-232 port, no external power source is required. The modem has it’s own micropower voltage regulator, allowing it to operate from a single polarity unregulated power source as low as +4.8 volts. Thus it can be powered directly from the +5 volt logic supply in microcontroller applications.

The RTX-12 is available in two different versions: The RTX-12A and the RTX-12OEM. Both versions are functionally and electrically identical. The only difference between them is their physical layout and the connectors used for the radio and data interfaces. The RTX-12A is packaged in a custom injection molded case and is designed to plug directly into a standard 25-pin RS-232 serial port. Connection to the radio is through an RJ-11 connector and cable (included). The RTX-12OEM model is intended for embedded applications and is provided without an enclosure. This modem is extremely small (1-1/4” x 1-1/2”) and is easily installed inside other equipment. A single 10-pin header provides connections for both the radio and data interface. An optional color coded ribbon cable is available for this modem.

Both the RTX-12A and the RTX-12OEM are normally supplied with full transmit and receive capability. However, in high volume applications either modem can be specially ordered in a Transmit or Receive Only version at reduced cost.

If you have any questions about the RTX-12 modems, please see our RTX-12 FAQ or contact our Technical Support Department.

RTX-12A CONNECTIONS:

Pin #2 (TXD) - Transmit Data            Level:    RS-232 (+/- 15v max)
                                                                       CMOS (0/+5v typ)

Pin #3 (RXD) - Receive Data             Level:    RS-232 (+/- 3v min)
                                                                       CMOS (0/+4.5v typ)

Pin #4 (RTS) - Negative In / PTT       Level:    RS-232 (+/- 4.5v min)
                                                                       CMOS (0/+4.5v typ)

Pin #6 (DSR) - Carrier Detect            Level:    RS-232 (+/- 3v min)
                                                                       CMOS (0/+4.5v typ)

Pin #7 (GND) - Power/Digital Ground

Pin #20 (DTR) - Positive Supply        Input:     +4.8 volts (min)
                                                                       +15 volts (max)
                                                                       5 millamperes (typ)

Radio Connector (RJ-11):

Pin #1 (Yellow) - Mic audio Output             Level:        0 - 290 mv p-p (Hi Z)
                                                                                    0 - 80 mv p-p (1K ohm)
                                                                                    Factory set @ 20 mv p-p (1K ohm)

Pin #2 (Green) - Receive Audio Input          Level:        300 mv p-p (nom)
                                                                                    780 mv p-p (max)
                                                                   Input Z:     50K (typ)

Pin #3 (Red) - PTT Output Output              Level:                  Sink 50ma (max)
                                                                   Output Voltage:   15 volts (max)
                                                                   Output Type:       Open Drain (FET)

Pin #4 (Black) - Ground “HT” Jumper - Connects 2.7K resistor between the PTT and Mic Audio lines for keying most hand-held radios. See notes in “HT” section.

“LEVEL” - Adjustment on modem that adjusts transmit audio (deviation) level.

RTX-12OEM CONNECTIONS:

Pin #1 (GND) - Power/Digital Ground (Brown)

Pin #2 (DTR) - Positive Supply        Input:    +4.8 volts (min) (Red)
                                                                    +15 volts (max)
                                                                    5 millamperes (typ)

Pin #3 (RXD) - Receive Data          Level:    RS-232 (+/- 3v min) (Orange)
                                                                    CMOS (0/+4.5v typ)

Pin #4 (DSR) - Carrier Detect         Level:    RS-232 (+/- 3v min) (Yellow)
                                                                    CMOS (0/+4.5v typ)

Pin #5 (TXD) - Transmit Data         Level     RS-232 (+/- 15v max) (Green)
                                                                    CMOS (0/+5v typ)

Pin #6 (RTS) - Negative In / PTT    Level:    RS-232 (+/- 4.5v min) (Blue)
                                                                    CMOS (0/+4.5v typ)

Radio Connector (10-pin header):

Pin #7 - Receive Audio Input           Level:        300 mv p-p (nom) (Violet)
                                                                        780 mv p-p (max)
                                                       Input Z:     50K (typ)

Pin #8 - PTT Output Output            Level:                   Sink 50ma (max) (Gray)
                                                       Output Voltage:    15 volts (max)
                                                       Output Type:        Open Drain (FET)

Pin #9 - Mic audio Output               Level:        0 - 290 mv p-p (Hi Z) (White)
                                                                        0 - 80 mv p-p (1K ohm)
                                                                        Factory Set @ 20 mv p-p (1K ohm)

Pin #10 - Ground (Black) “HT” Jumper - Connects 2.7K resistor between the PTT and Mic Audio lines for keying most hand-held radios. See notes in “HT” section.

“LEVEL” - Adjustment on modem that adjusts transmit audio (deviation) level.

GENERAL SPECIFICATIONS:

Levels (Data):          RS232 (+/- 3v min)
                               CMOS (2.5v min / 5v max)

Power Supply:         +4.8v (min), +12v (max) 2.5ma

Operating Mode:     Simplex or half duplex

Compatibility:          Bell 202 (Opt. CCITT v.23)

Dimensions:             Standard:    2.1” x 2.4” x .72”
                               OEM:         1.25” x 1.50” x .45”

Connectors:            Standard: DB-25S / RJ-11
                              OEM: 10 pin header (.1” cent)

Operating Temp:    -30C to +60C

OPTIONS:

Input Level:      ** Factory installed option for low input impedance or increased input level.

Output Level:   ** Option to increase or decrease output modulation level.

Receive Only:   ** Modem without transmit circuitry.

Transmit Only:  ** Modem without receive circuitry.

** These options available on quantity purchases only.

Note: Contact the factory regarding special configurations, such as Transmit or Receive Only versions. We welcome the opportunity to quote any other special modifications that you may require.

MODEL NUMBERS:

With CCITT v.23: Add “V23” to part number (RTX-12AV23) (RTX-12OEMV23)

Cable for OEM: OEMCAB1 (6” Colored Ribbon w/IDC)

RTX-12OEM CIRCUIT BOARD DIMENSIONS:

Additional Information:

• See Price List and Ordering Information.

• View the RTX Frequently Asked Questions page.

• Download The Installation Manual from Telemetry Modem Support Page.